Bone health depends on the coordinated activities of bone forming osteoblasts and bone resorbing osteoclasts. “Bone turnover reflects a balance between these anabolic and catabolic cellular functions and ensures that the mature skeleton can repair itself when damaged and sustain its endocrine function by release of minerals such as calcium and phosphorous into the circulation.” Allen, J. G. et al., J. Med. Chem., 53 (Jun. 10, 2010), pp. 4332-4353, 4332. Many disease states alter this balance, resulting in increased or decreased bone mass or changes in bone quality. Gradual loss of bone mineral density is known as osteopenia; severe loss of bone is known as osteoporosis. Id.
The current standard of care for the treatment and prevention of osteoporosis utilizes the bisphosphonate class of oral, small molecule antiresportives. Id. at 4333. Zoledronic acid, raloxifene, calcium, and vitamin D supplements are also typically used in the osteoporosis treatment. Id. While antiresporptive agents can help prevent bone loss, anabolic agents “are capable of increasing bone mass to a greater degree . . . and also have the capacity to improve bone quality and increase bone strength.” Guo, H., et al., J. Med. Chem., 53 (Feb. 25, 2010), pp. 1819-1829, 1819. In the United States, human PTH is the only FDA-approved anabolic agent. Id.; Allen at 4333. “Because of the paucity of available anabolic agents for osteoporosis treatment, there is an urgent need to develop small molecular compounds to treat this disease that are nontoxic, cost-effective, and easy to administer.” Guo, at 1819.
“Although the development of pharmacological agents that stimulate bone formation is less advanced compared to antiresporptive therapies, several pathways are known to facilitate osteoblast function.” Allen at 4338. These pathways include bone morphogenic proteins, transforming growth factor β, parathyroid hormone, insulin-like growth factor, fibroblast growth factor, and wingless-type MMTV integration site (WNT) signaling. Id.Guo and coworkers recently reported results concerning the first of these pathways. Guo, supra. In particular, they reported that certain substituted benzothiophene and benzofuran compounds enhance bone morphogenic protein 2 expression in mice and rats. Two of the compounds reportedly stimulate bone formation and trabecular connectivity restoration in vivo. Id. at 1819.
Another of these pathways is the WNT pathway, which is implicated in a variety of developmental and regenerative processes. Allen at 4340. The pathway is complex, however, and much about it and about how its components affect bone remains unclear. For example, it has been suggested that LRP-5, mutations of which are associated with increased bone mass in humans, and β-catenin, through which canonical WNT signaling occurs, “may not be linked directly via WNT signaling to the control of bone mass.” Id.
Recent analysis of gene expression data has led to the identification of new targets of WNT signaling. See, e.g., Torisu, Y., et al., Cancer Sci., 99(6):1139-1146, 1143 (2008). One such target is Notum Pectinacetylesterase, also known as NOTUM and LOC (174111).